There has long been known a method for producing a material releasable from sticky substances such as pressure-sensitive adhesive by forming a releasable cured film formed on a surface of a substrate such as paper, laminated paper, and plastic film. The material used for forming the releasable cured film is a silicone composition. For example, a silicone release coating composition of condensation reaction curing type, which is composed of silanol group-containing organopolysiloxane, organohydrogenpolysiloxane, and tin compound, was disclosed in JP-B S35-13709 (Patent Documents 1) and JP-B S36-1397 (Patent Documents 2).
The pioneering material mentioned above was followed by a composition of addition reaction curing type as disclosed in JP-B S46-26798 (Patent Document 3). This new composition soon came into general use on account of its better curability and longer pot life than the old condensation type. The addition curing type is still prevailing especially in the application for release paper which needs curing at a comparatively low temperature within a short time.
The coating composition of condensation reaction curing type mentioned above usually employs a tin compound in the form of alkyl tin which is superior in curing performance, colorless, liquid, and soluble in silicone. Unfortunately, this tin compound is toxic (to reproduction). Moreover, it is pointed out that the tin compound as a suspected environmental hormone is harmful to the environment, and hence there has been a movement to limit the use of the tin compound more strictly.
Despite its disadvantage mentioned above, the coating composition of condensation reaction curing type has advantages of finding use in an area where addition reaction curing type suffers from catalytic poison and of being cable of being used in mixture with a variety of other materials. Therefore, it is expected that the silicone release coating composition of condensation reaction curing type will find use in varied areas if it is relieved from problems with safety of tin catalyst and environmental load.
Consequently, much has been studied for the development of non-tin catalysts. Some examples are listed below:
quaternary phosphonium hydroxide compound, disclosed in JP-A S59-176326 (Patent Document 4);
quaternary ammonium ion compound, disclosed in WO 2008/081890 (Patent Document 5);
organic substance such as guanidine, disclosed in U.S. Pat. No. 3,719,633 (Patent Document 6), U.S. Pat. No. 4,180,462 (Patent Document 7), and JP-T 2011-506584 (Patent Document 8); and
natural mineral such as kaolin, disclosed in JP-T 2011-510103 (Patent Document 9).
Conventional metal compounds include titanium and zinc compounds. Recently proposed metal compounds are listed below:
Ir compound, disclosed in JP-T 2007-527932 (Patent Document 10);
Zr compound, disclosed in JP-A 2010-163602 (Patent Document 11);
Zn compound, disclosed in JP-T 2011-506738 (Patent Document 12);
Mo compound, disclosed in JP-T 2011-506744 (Patent Document 13); and
various metals such as Cu, Ag, B, Sc, Ce, Bi, Ge, and Mn, disclosed in JP-T 2011-506739 (Patent Document 14).
Such metal catalysts, however, are less common in the industry than tin catalysts because of their slow reaction rate, tendency toward gelation, poor catalytic effect, and high cost. These disadvantages prevent their use especially for the silicone release coating agent which needs curing at a comparatively low temperature within a short time.